Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment, as examples. Semiconductor devices are typically fabricated by sequentially depositing insulating or dielectric layers, conductive layers, and semiconductive layers of material over a semiconductor substrate, and patterning the various layers using lithography to form circuit components and elements thereon.
A transistor is an element that is used frequently in semiconductor devices. There may be millions of transistors on a single integrated circuit (IC), for example. A common type of transistor used in semiconductor device fabrication is a metal oxide semiconductor field effect transistor (MOSFET), as an example. A transistor typically includes a gate dielectric disposed over a channel region in a substrate, and a gate electrode formed over the gate dielectric. A source region and a drain region are formed on either side of the channel region within the substrate.
Complementary metal oxide semiconductor (CMOS) devices utilize both positive and negative channel transistor devices in complementary configurations. The positive and negative channel devices of CMOS devices are typically referred to as p channel metal oxide semiconductor (PMOS) field effect transistors (PFETs) and n channel metal oxide semiconductor (NMOS) field effect transistors (NFETs), for example. A PFET is formed in an n well (e.g., a well implanted with n type dopants) and an NFET is formed in a p well. An isolation region such as a shallow trench isolation (STI) region is formed between the n well and p well of the PFET and the NFET, respectively.
What are needed in the art are improved methods of fabricating semiconductor devices including transistors and structures thereof.